This invention relates to an improvement in a process for preparing a product predominant in decabromodiphenylalkane. More particularly, this invention relates to a method and apparatus for heat-treating a product predominant in decabromodiphenylethane in order to reduce the amount of unreacted bromine in the product.
Polyhalogenated diphenylalkanes, e.g. decabromodiphenylethane, are known flame retardants for use in polyolefin and polystyrenic-based formulations. On a commercial basis, the polyhalogenated diphenylalkane is supplied to the formulation as a product predominant in the polyhalogenated diphenylalkane selected. The product would have a form and an impurity content which would be characteristic of the process used to produce it. If the product's physical characteristics, e.g. thermal stability, limit the formulation's processability, then the processor's desire for the product is limited at best. If the product's color is not white or at least near white, the product will be suitable for use in some formulations, however, the product's use may not be acceptable in formulations calling for a white or light color.
When preparing a polybrominated diphenylalkane predominant product such as decabromodiphenylethane, there is a tendency for the product to retain a substantial amount of unreacted bromine even after separation of the product from the reaction mass and drying. By "substantial amount" is meant more than about 1000 ppm bromine. Such a high content of unreacted bromine leads to a product having a color characteristic which is less desirable than products having much lower bromine contents. Until now, conventional drying and grinding techniques, such as disclosed by Ayres et al., U.S. Pat. No. 4,327,227 and Bark et al., U.S. Pat. No. 4,659,021 have been less successful in reducing a substantial amount of unreacted bromine in the isolated product.